Study to evaluate the safety and efficacy of asciminib in pediatric participants with chronic myeloid leukemia.

Prior treatment

• Known second chronic phase of CML after previous progression to Accelerated Phase (AP)/Blast Phase (BP).
• Previous treatment with a hematopoietic stem-cell transplantation.
• Patient planned to undergo allogeneic hematopoietic stem cell transplantation
• Known presence of a BCR::ABL mutation with known resistance to study treatment in accordance with the most recent public version of international CML clinical guidelines (e.g. NCCN CML treatment guidelines v 1.2026 and Apperley et al 2025) at any time prior to study entry.

• Signed informed consent must be obtained prior to participation in the study
• Male or female participants 1and <18 years of age at study enrollment
• Diagnosis of CML-CP (Apperley et al 2025) with cytogenic confirmation of Philadelphia positive (Ph+) chromosome
• For participants with CML-CP newly diagnosed within 3 months of screening
• For participants with CML – CP with high risk of developing resistance or intolerance to previous TKI a. Unfavourable response to TKI is defined following the Apperley et al 2025 Guidelines as: · At three months after the initiation of therapy: BCR::ABL1 ratio > 10% IS (if confirmed within 1-3 months) · At six months after the initiation of therapy: BCR::ABL1 ratio > 10% IS · At twelve months after initiation of therapy: BCR::ABL1 ratio > 1% IS · At any time loss of previous response · At any time emergent resistant BCR::ABL1 mutations or high-risk ACA from prior TKI treatment as per local test results b. Intolerance to TKI is defined as: · Non-hematologic intolerance: participants with grade 3 or 4 toxicity while on therapy (in which case the patient is eligible whether or not there was a dose reduction); or with persistent grade 2 toxicity unresponsive to optimal management including dose adjustments (unless dose reduction is not considered in the best interest of the patient if response is already suboptimal) · Hematologic intolerance: participants with grade 3 or 4 toxicity (absolute neutrophil count [ANC] or platelets) while on therapy that is recurrent after dose reduction to the lowest doses of the TKI
• Evidence of typical BCR::ABL1 transcript [e14a2 and/or e13a2] at the time of screening which are amenable to standardized RQ-PCR quantification.
• Performance status: Karnofsky ≥ 50% for participants ≥ 16 years of age, and Lansky ≥ 50 for participants < 16 years of age at the time of screening.